// Loaded from https://raw.githubusercontent.com/nats-io/nkeys.js/v1.0.0-7/src/crc16.ts


/*
 * Copyright 2018-2020 The NATS Authors
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

// An implementation of crc16 according to CCITT standards for XMODEM.
/**
 * @ignore
 */
const crc16tab = new Uint16Array([
  0x0000,
  0x1021,
  0x2042,
  0x3063,
  0x4084,
  0x50a5,
  0x60c6,
  0x70e7,
  0x8108,
  0x9129,
  0xa14a,
  0xb16b,
  0xc18c,
  0xd1ad,
  0xe1ce,
  0xf1ef,
  0x1231,
  0x0210,
  0x3273,
  0x2252,
  0x52b5,
  0x4294,
  0x72f7,
  0x62d6,
  0x9339,
  0x8318,
  0xb37b,
  0xa35a,
  0xd3bd,
  0xc39c,
  0xf3ff,
  0xe3de,
  0x2462,
  0x3443,
  0x0420,
  0x1401,
  0x64e6,
  0x74c7,
  0x44a4,
  0x5485,
  0xa56a,
  0xb54b,
  0x8528,
  0x9509,
  0xe5ee,
  0xf5cf,
  0xc5ac,
  0xd58d,
  0x3653,
  0x2672,
  0x1611,
  0x0630,
  0x76d7,
  0x66f6,
  0x5695,
  0x46b4,
  0xb75b,
  0xa77a,
  0x9719,
  0x8738,
  0xf7df,
  0xe7fe,
  0xd79d,
  0xc7bc,
  0x48c4,
  0x58e5,
  0x6886,
  0x78a7,
  0x0840,
  0x1861,
  0x2802,
  0x3823,
  0xc9cc,
  0xd9ed,
  0xe98e,
  0xf9af,
  0x8948,
  0x9969,
  0xa90a,
  0xb92b,
  0x5af5,
  0x4ad4,
  0x7ab7,
  0x6a96,
  0x1a71,
  0x0a50,
  0x3a33,
  0x2a12,
  0xdbfd,
  0xcbdc,
  0xfbbf,
  0xeb9e,
  0x9b79,
  0x8b58,
  0xbb3b,
  0xab1a,
  0x6ca6,
  0x7c87,
  0x4ce4,
  0x5cc5,
  0x2c22,
  0x3c03,
  0x0c60,
  0x1c41,
  0xedae,
  0xfd8f,
  0xcdec,
  0xddcd,
  0xad2a,
  0xbd0b,
  0x8d68,
  0x9d49,
  0x7e97,
  0x6eb6,
  0x5ed5,
  0x4ef4,
  0x3e13,
  0x2e32,
  0x1e51,
  0x0e70,
  0xff9f,
  0xefbe,
  0xdfdd,
  0xcffc,
  0xbf1b,
  0xaf3a,
  0x9f59,
  0x8f78,
  0x9188,
  0x81a9,
  0xb1ca,
  0xa1eb,
  0xd10c,
  0xc12d,
  0xf14e,
  0xe16f,
  0x1080,
  0x00a1,
  0x30c2,
  0x20e3,
  0x5004,
  0x4025,
  0x7046,
  0x6067,
  0x83b9,
  0x9398,
  0xa3fb,
  0xb3da,
  0xc33d,
  0xd31c,
  0xe37f,
  0xf35e,
  0x02b1,
  0x1290,
  0x22f3,
  0x32d2,
  0x4235,
  0x5214,
  0x6277,
  0x7256,
  0xb5ea,
  0xa5cb,
  0x95a8,
  0x8589,
  0xf56e,
  0xe54f,
  0xd52c,
  0xc50d,
  0x34e2,
  0x24c3,
  0x14a0,
  0x0481,
  0x7466,
  0x6447,
  0x5424,
  0x4405,
  0xa7db,
  0xb7fa,
  0x8799,
  0x97b8,
  0xe75f,
  0xf77e,
  0xc71d,
  0xd73c,
  0x26d3,
  0x36f2,
  0x0691,
  0x16b0,
  0x6657,
  0x7676,
  0x4615,
  0x5634,
  0xd94c,
  0xc96d,
  0xf90e,
  0xe92f,
  0x99c8,
  0x89e9,
  0xb98a,
  0xa9ab,
  0x5844,
  0x4865,
  0x7806,
  0x6827,
  0x18c0,
  0x08e1,
  0x3882,
  0x28a3,
  0xcb7d,
  0xdb5c,
  0xeb3f,
  0xfb1e,
  0x8bf9,
  0x9bd8,
  0xabbb,
  0xbb9a,
  0x4a75,
  0x5a54,
  0x6a37,
  0x7a16,
  0x0af1,
  0x1ad0,
  0x2ab3,
  0x3a92,
  0xfd2e,
  0xed0f,
  0xdd6c,
  0xcd4d,
  0xbdaa,
  0xad8b,
  0x9de8,
  0x8dc9,
  0x7c26,
  0x6c07,
  0x5c64,
  0x4c45,
  0x3ca2,
  0x2c83,
  0x1ce0,
  0x0cc1,
  0xef1f,
  0xff3e,
  0xcf5d,
  0xdf7c,
  0xaf9b,
  0xbfba,
  0x8fd9,
  0x9ff8,
  0x6e17,
  0x7e36,
  0x4e55,
  0x5e74,
  0x2e93,
  0x3eb2,
  0x0ed1,
  0x1ef0,
]);

/**
 * @ignore
 */
export class crc16 {
  // crc16 returns the crc for the data provided.
  static checksum(data: Uint8Array): number {
    let crc: number = 0;
    for (let i = 0; i < data.byteLength; i++) {
      let b = data[i];
      crc = ((crc << 8) & 0xffff) ^ crc16tab[((crc >> 8) ^ (b)) & 0x00FF];
    }
    return crc;
  }

  // validate will check the calculated crc16 checksum for data against the expected.
  static validate(data: Uint8Array, expected: number): boolean {
    let ba = crc16.checksum(data);
    return ba == expected;
  }
}
